Replace default export with named exports (#1998)

## Launch Checklist

See title,
Also removed some "_" from some file names.
This is a pure refactoring, no logic changes.


 - [x] Briefly describe the changes in this PR.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/components/Collapser.tsx

@@ -6,7 +6,7 @@ type CollapserProps = {
   style?: object
 };
 
-export default class Collapser extends React.Component<CollapserProps> {
+export class Collapser extends React.Component<CollapserProps> {
   render() {
     const iconStyle = {
       width: 20,